1. Field of the Invention
The present invention relates, in general, to explosives and explosives manufacturing.
2. Background Art
In the field of explosives and explosives manufacturing, there are many types of explosives made for various applications. A few of these applications are for mining, construction, demolition, law enforcement and military uses. There are a multitude of explosive products available to satisfy the requirements in these fields. For example, for blasting rock in mining and construction work, the user can choose from cartridged explosives such as dynamite, water-gels and emulsions which are used for small diameter bore holes (up to 3 inches). For larger boreholes, blasting agents are used in the form of Ammonium Nitrate/Fuel Oil mixtures (ANFO), which are poured or pumped into position. Unlike the smaller, “cap-sensitive” cartridged explosives, these blasting agents (by definition) require a small, high explosive booster to initiate the detonation thereof.
For commercial demolition applications, cartridged explosives are placed in small boreholes within concrete columns and beams in the case of buildings, bridges and other similar structures. Where steel needs to be cut, small but powerful high explosive shaped charges are used to sever critical points in order to complete the demolition.
Military applications for explosives are many. However, they tend to fall into two main groups. The first is for bombs, artillery shells, mortars, mines, etc. For these uses, the explosives are generally placed into the devices by means of a melt-pour operation. The second group are explosives used for demolition and breaching by Special Forces and engineering groups. Although some of the explosive charges are pre-made devices incorporating shaped charge or Explosively Formed Projectile (EFP) technology, most are simply bulk explosives in the form of blocks (C-4, and TNT) or sheets (Deta-Sheet).
Another military related use of explosives is demining operations and unexploded ordnance (UXO) clearing operations where explosive charges are used to sympathetically detonate and destroy landmines as well as “dud” bombs and artillery shells. Similar type work conducted by civilian contractors after a conflict has been termed “Humanitarian Demining”. Clearing of old military firing ranges by these contractors is called remediation.
Although the previously mentioned applications consume the bulk of the explosives used in the world, smaller quantities are also used for the following purposes:
Agricultural blasting such as tree stump removal, irrigation and drainage ditch blasting and beaver dam control;                Avalanche control;        Metal hardening;        Forest fire fighting;        Submarine (underwater) blasting;        Seismic work;        Secondary blasting such as boulder breaking;        Law enforcement applications such as tactical breaching and bomb squad work.        
Due to threats of terrorism and increased attention to accident prevention, regulations concerning the transportation, storage, use and transfer relating to explosives have steadily increased over the last few years. Along with this has come an increase in the cost of using explosives, particularly, in the area of transportation.
Where explosives are used in volume, such as mines and quarries, the cost of transporting a truckload of explosives is not much more than a truckload of any other material. However, where small amounts of explosives are required, the transportation costs can far exceed the cost of the product. For example, it costs just as much to transport one stick of dynamite by commercial truck as it does two thousand pounds of dynamite. In order to accommodate the user who needs smaller quantities to do a job, “binary” or “two-part” explosives are available. One popular brand is called Kinepak. It appears that this product is based on U.S. Pat. No. 3,718,512 by Hurst. As described in the Hurst patent and embodied in the commercially available product Kinepak, two individual, nonexplosive components are combined by the user to form a cap sensitive explosive. The first component, referred to as “the liquid” is predominantly nitromethane (NM). The other component, referred to as “the solid” is primarily finely divided ammonium nitrate (AN). The commercial product Kinepak is packaged in several different sizes and shapes of plastic bottles as well as foil pouches (bags) which are intended for various applications. In each case, the solid component container is supplied with an appropriate amount of premeasured liquid in another individual container.
The liquid component of the Kinepak is classified as a “Flammable Liquid” for transportation purposes. The solid component is classified as an “Oxidizer”. Although both are considered hazardous materials, neither is defined as an explosive for transportation (U.S. Department of Transportation, DOT regulations) or storage (U.S. Bureau of Alcohol, Tobacco and Firearms, ATF regulations).
In order to use Kinepak, the liquid component is simply poured into the solid component. Within about five to fifteen minutes, the liquid (which is usually colored red) will soak down to the bottom of the container, as evidenced by the pink color. At this point, it has the consistency of moist powder and is a cap sensitive, high explosive. It can be used in most situations where it would be suitable to use cartridged explosives such as dynamite, water gels and small diameter emulsions.
Kinepak is used as an example here because it is, at the time of this writing, one of the only two commercially available two-component explosives. The only other known commercial product is marketed under the name Binex. It is believed to be based upon U.S. Pat. No. 5,226,986 to Hansen, et al. Binex uses a two component system of an aqueous solution of sodium perchlorate and aluminum powder. When these two components are combined, a liquid explosive is formed that is cap sensitive. It is believed that this composition would not be a viable product as a replacement for cartridged explosives because of the high cost and the environmental concerns with the sodium perchlorate solution. However, there is a current military application where this product is used to blast fox holes in conjunction with an entrenchment kit for soldiers. It is known that this explosive has detonation velocity that is much lower than Kinepak and other commercial cartridged explosives. In the case of the military application, this is an advantage as lower velocity explosives are generally better for cratering in soil.
There are many other possible candidates for use as binary explosives. However, most of these others would not be viable for consideration as commercial products for the following reasons:                toxicity of the components and/or detonation products;        stability of the components before and after mixing;        shelf life;        cost;        ease/difficulty of mixing;        no advantages when compared to ammonium nitrate/nitromethane systems (Kinepak).        
In most binary systems, like the ones mentioned previously, one of the components is an oxidizer (ammonium nitrate, sodium perchlorate) and the other is a fuel (nitromethane, aluminum). As with all explosives, the potential uses and effects are determined by several properties such as detonation velocity, density, gas production, etc. Effects on a specific target can be influenced by container size, shape and confinement. For example, configuring the explosive in a shaped charge container will cause more of the available energy to be focused toward a given target than would be possible otherwise. The type of initiation system required and utilized will also have an effect, especially with blasting agents such as ANFO.
Ammonium nitrate and nitromethane (AN-NM) binary systems such as Kinepak work very well for their intended purpose. They have the following advantages over conventional explosives:                The components are not explosives before mixing;        The components do not have to be transported as explosives;        The components do not have to be stored as explosives (in most places) therefore do not require expensive storage “magazines”.        
The above listed advantages are due to the fact that they are mixed on site just before using.
However, there are a few disadvantages:                Mixing can be time consuming;        Shelf life of the ammonium nitrate powder can be short depending on conditions, particularly temperature;        Can cost 2 to 3 times more than conventional explosives (this must be weighed against the advantages above).        
As mentioned previously, although other systems besides AN-NM exist, there has not been a commercially viable product available as a substitute for conventional small diameter cartridge explosives.
There are other binary systems based on nitroparaffins such as nitromethane, nitroethane, nitropropanes, etc. These nitroparaffins are very interesting materials. Under the right circumstances, they can act as a fuel (as when combined with ammonium nitrate) an oxidizer or a stand alone explosive, especially nitromethane. However, as will be discussed later, they are too insensitive to be used as explosives as is.
There are several patents that attempt to utilize nitroparaffins as the basis of a binary system. In U.S. Pat. No. 3,338,165 Minnick teaches how to make stable explosive compositions by adding a sensitizer, in the form of resin balloons, to nitromethane. He mentions in the patent that it is well known that amines (particularly ethylenediamine) will sensitize nitromethane so that it will detonate with a blasting cap. He continues to say that these mixtures become unstable and decompose after a few days. Not mentioned is that most of these sensitizing agents are very toxic and difficult to work with safely. The basis of this patent is that by entrapping air into the nitromethane liquid, by means of micro balloons (resin, glass, etc.), it can be made cap-sensitive. However since the balloons will float to the surface of pure nitromethane, a thickening (gelling) agent must be added to prevent this.
Another U.S. Pat. No. 3,977,921 by Chandler seeks to overcome some of the problems of using the balloon method of Minnick by achieving air entrapment sensitization by means of an open celled polymeric foam material.
U.S. Pat. No. 4,925,505 of Baker, et al., discloses a means of making a foamable nitromethane composition by the addition of stabilizers, thickeners, sensitizing and foaming agents. It also teaches the addition of metals, including aluminum, to enhance the total energy of the system. The idea of this invention was that the foam would be applied to a mine field and then detonated. Two problems with this method is the very low density of the foam, thus low velocity. Another problem is the useable life of the foam after its application. This would greatly vary depending on conditions such as temperature, wind, sunlight, etc.
To those skilled in the art, it is commonly known that the addition of aluminum to many explosive compositions (usually water gels) not only adds energy, but also increases its sensitivity. As described in U.S. Pat. No. 4,115,165, Machacek describes such an addition of aluminum to typical water gel mixtures (nitromethane is not mentioned in this patent). Further, Machacek teaches the use of aluminum coated with stearic acid which give it a hydrophobic property. This causes air bubbles to cling to the surface of the aluminum particles. As noted before, the incorporation of air bubbles into explosive mixtures increases the sensitivity.
U.S. Pat. No. 5,226,986, previously cited, also explains the use of mixtures of nitromethane and nitroethane as the oxidizing liquid and aluminum fuel granules having an average particle size within the range of 1/64 to ¼ inch and an average bulk density within the range of 0.2 to 1.0 grams/cc. Also, this patent describes the resultant explosive as being a blasting agent requiring a one pound booster for initiation, not a cap sensitive, small diameter mixture.
U.S. Pat. No. 6,405,627 by Anderson describes a kit for demining operations utilizing sensitized nitroparaffins, to include nitromethane and nitroethane, as the explosive means. As with previous patents, the use of microspheres is the primary method of sensitization. The patent also describes the use of fumed silica as a thickening agent. In claim 12, Anderson also mentioned the addition of powdered aluminum in addition to the microspheres. In the description of the patent, he does not explain the purpose of the aluminum.
(25) References Cited:U.S. patents3,338,165August 1967Minnick3,718,512February 1973Hurst3,977,921August 1976Chandler4,115,165September 1978Machacek4,925,505May 1990Baker, et al.5,226,986July 1993Hansen, et al.6,405,627June 2002Anderson
Pure nitromethane is actually a very powerful explosive. However, without the addition of some additives or modifiers, it is so insensitive that it is classified as a “Flammable Liquid” for transportation purposes. Pure nitromethane will not usually detonate unless it is subjected to extreme shock and/or confinement at elevated temperatures. Most of the efforts to make a usable nitromethane based explosive have centered on adding dangerous amine compounds and/or incorporating entrapped air bubbles by some means. These air bubbles, while having the desired result of sensitization, have the undesired result of decreasing the density, and thereby lowering the velocity. Further, since these air bubble means are non-energetic, the per unit volume energy is also decreased.
There is a need for another high energy, binary explosive compound. Although ammonium nitrate and nitromethane systems provide a good product, a binary explosive with a higher velocity and total energy would be able to perform tasks that are currently not possible. There are many commercial and military applications where such an explosive would be very useful. If this new binary explosive was in liquid form after mixing, it would be particularly attractive because of its ability to be poured into and fill any container.